The use of an air deflector which is able to be fixed either to a windshield wiper blade, or to a wiper arm carrying such a blade, is necessary in order to prevent disengagement of the blade from the glass which is being swept. Such disengagement is caused by aerodynamic forces set up by air flows impinging on the wiper blade, when the vehicle which carries the windshield wiper assembly comprising the blade and its arm is travelling at high speed while the wiper is operating.
Such a deflector should have its free edge directed towards the swept surface, typically the windshield of the vehicle, and it should also be as close to this surface as possible so as to reduce to a minimum the space between the swept surface and that edge of the deflector. This is because it is necessary to prevent air flows being able to force their way into this space in such a way as to tend to set up an aerodynamic force on the back face of the deflector, which would then cause the wiper to lift away from the surface. However, such proximity is limited, partly by the curvature of the windshield and partly by the risk of contact of the free edge of the air deflector with the windshield itself, which can cause damage to the swept surface of the latter, with eventual detriment to good visibility by the driver. It has been proposed, in particular in the published patent application No. DE 3 637 348A of the Federal Republic of Germany, to make the free edge of an air deflector in a material which is substantially softer than the rest of the deflector. This arrangement necessitates the manufacture of a deflector in two materials, with difficulties then arising of joining these two materials together. In addition, when the wiper is in operation, and due to the curvature of the windshield, the deflector runs the risk of assuming a position such that its softer free edge no longer lies facing towards the swept surface, so that it is in fact the harder part which is in danger of coming into contact with the swept surface.